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Unformatted text preview: mcconnell (kam2342) oldhomework 07 Turner (60230) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Through what potential difference would an electron need to be accelerated for it to achieve a speed of 3 . 2 % of the speed of light (2 . 99792 10 8 m / s), starting from rest? Correct answer: 261 . 632 V. Explanation: Let : s = 3 . 2% = 0 . 032 , c = 2 . 99792 10 8 m / s , m e = 9 . 10939 10- 31 kg , and q e = 1 . 60218 10- 19 C . The speed of the electron is v = 0 . 032 c = 0 . 032 ( 2 . 99792 10 8 m / s ) = 9 . 59336 10 6 m / s , By conservation of energy 1 2 m e v 2 =- (- q e ) V V = m e v 2 2 q e = ( 9 . 10939 10- 31 kg ) ( 9 . 59336 10 6 m / s ) 2 2 (1 . 60218 10- 19 C) = 261 . 632 V . 002 (part 1 of 3) 10.0 points Consider two concentric spherical conducting shells. The smaller shell has radius a = 0 . 2 m and charge 8 C on it, while the larger shell has radius b = 3 a and charge 40 C on it. Assume that the electric potential V at is zero. The Coulomb constant is 8 . 98755 10 9 N m 2 / C 2 . b = 3a a #1 #2 P q 1 q 2 O Determine the electric field E at P, where the distance OP = 2 a . Correct answer: 4 . 49378 10 5 N / C. Explanation: Let : a = 0 . 2 m , q 1 = 8 C = 8 10- 6 C , q 2 = 40 C = 4 10- 5 C , and k = 8 . 98755 10 9 N m 2 / C 2 . Set up a Gaussian surface of radius r = 2 a between the shells. Due to symmetry, the electric field is constant over the surface of the sphere, so the flux is simply = E A . The enclosed charge is q 1 . From Gausss Law, = Q encl E 4 r 2 = q 1 , and r = 2 a , so E = q 1 4 (2 a ) 2 = k q 1 4 a 2 = ( 8 . 98755 10 9 N m 2 / C 2 ) 8 10- 6 C 4 (0 . 2 m) 2 = 4 . 49378 10 5 N / C . 003 (part 2 of 3) 10.0 points Find the electric potential V at point P . 1. 1 4 parenleftBig q 1 3 a + q 2 2 a parenrightBig 2. 1 4 parenleftbigg q 1 + q 2 2 a parenrightbigg 3. 1 4 parenleftBig q 1 2 a + q 2 3 a parenrightBig correct mcconnell (kam2342) oldhomework 07 Turner (60230) 2 4. 1 4 parenleftBig q 1 2 a + q 2 a parenrightBig 5. 1 4 parenleftbigg q 1 + q 2 3 a parenrightbigg 6....
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This note was uploaded on 11/22/2010 for the course PHYS 303 taught by Professor Turner during the Spring '10 term at University of Texas.

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oldhw7_pdf - mcconnell(kam2342 oldhomework 07 Turner(60230...

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